Constant entrance hole perforating gun system and method

ABSTRACT

A shaped charge comprising a case, a liner positioned within the case, and an explosive filled within the case. The liner is shaped with a subtended angle ranging from 100° to 120° about an apex, a radius, and an aspect ratio such that a jet formed with the explosive creates an entrance hole in a well casing. The jet creates a perforation tunnel in a hydrocarbon formation, wherein a diameter of the jet, a diameter of the entrance hole diameter, and a width and length of the perforation tunnel are substantially constant and unaffected with changes in design and environmental factors such as a thickness and composition of the well casing, position of the charge in the perforating gun, position of the perforating gun in the well casing, a water gap in the wellbore casing, and type of the hydrocarbon formation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of National Stage of PCT ApplicationNo. PCT/US2017/055791, filed Oct. 9, 2017, which is related to, andclaims priority from U.S. Utility application Ser. No. 15/352,191, filed15 Nov. 2016, which claims the benefit of U.S. Provisional ApplicationNo. 62/407,896, filed 13 Oct. 2016, the disclosures of which are fullyincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to perforation guns that areused in the oil and gas industry to explosively perforate well casingand underground hydrocarbon bearing formations, and more particularly toan improved apparatus for creating constant entry hole diameter andconstant width perforation tunnel.

PRIOR ART AND BACKGROUND OF THE INVENTION Prior Art Background

During a well completion process, a gun string assembly is positioned inan isolated zone in the wellbore casing. The gun string assemblycomprises a plurality of perforating guns coupled to each other eitherthrough tandems or subs. The perforating gun is then fired, creatingholes through the casing and the cement and into the targeted rock.These perforating holes connect the rock holding the oil and gas and thewellbore. During the completion of an oil and/or gas well, it is commonto perforate the hydrocarbon containing formation with explosive chargesto allow inflow of hydrocarbons to the wellbore. These charges areloaded in a perforation gun and are typically shaped charges thatproduce an explosive formed penetrating jet in a chosen direction.

As illustrated in FIG. 1 (0100), a perforating system with 3 clusters, 6shots or perforations per cluster in a well casing (0120) may be treatedwith fracturing fluid after perforating with the perforating system. Aplug (0110) may be positioned towards a toe end of the well casing toisolate a stage. Cluster (0101) may be positioned towards the toe end,cluster (0103) towards the heel end and cluster (0102) positioned inbetween cluster (0101) and cluster (0103). Each of the clusters maycomprise 3 charges. After a perforating gun system is deployed and thewell perforated, entrance holes are created in the well casing andexplosives create a jet that penetrates into a hydrocarbon formation.The diameter of the entrance hole further depends on several factorssuch as the liner in the shaped charge, the explosive type, thethickness and material of the casing, water gap in the casing,centralization of the perforating gun, number of charges in a clusterand number of clusters in a stage. A stage design may further bedesigned when the size of the entrance hole is determined with aspecific set of parameters. Parametric design means changing one thingat a time and evaluating the result. Parameters may be varied on acluster by cluster, a stage by stage, or a well by well basis. The fixedvariables may be fixed, the desired variables changed. The results areevaluated to determine a causality or lack thereof. However if severalfactors change, results appear to be random, and a conclusion may bedrawn to show that the change had no effect. Additionally a stage designdepends on the quality of perforation which include the entrance holesize and perforation tunnel shape, length and width. Due to the numberof factors that determine the entrance hole size, the variation of theentrance hole diameter (EHD) is large and therefore the design of astage becomes unpredictable. For example, an entrance hole that istargeted for 0.3 in might have a variation of +−0.15 and the resultingentrance hole diameter might be 0.15 or 0.45 inches. If the entrancehole diameter results in a lower diameter such as 0.15 inches, theresulting treatment may result in unintended and weak fractures in ahydrocarbon formation. Current designs are over designed for largerentrance hole diameters to account for the large variation due to theaforementioned factors affecting the EHD. The significant andunpredictable over design due to variation in EHD results inunpredictable costs, unreliable results and significant costs. Thereforethere is a need for a liner design that creates an entrance hole with adiameter that is unaffected by design and environmental factors such asa thickness of the well casing, composition of the well casing, positionof a charge in the perforating gun, position of the perforating gun inthe well casing, a water gap in the wellbore casing, or type of saidhydrocarbon formation. FIG. 1 (0100) illustrates variation in EHD ofvarious charges. For example, EHD (0131) in cluster (0103) issignificantly smaller than EHD (0121) in cluster (0102). Similarly thepenetration length and width of the perforation tunnel also vary withthe aforementioned design and environmental factors. For example,perforation tunnel (0113) in cluster (0103) may be longer thanperforation tunnel (0112) in cluster (0102). The large variation in thelength and width of the perforation tunnel further causes significantdesign challenges to effectively treat a hydrocarbon formation.Therefore there is a need to design a shaped charge comprising a linerfilled with an explosive such that the resulting variation in the lengthand the width of perforation tunnel is less than 7.5%.

FIG. 2A (0200) illustrates a chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versusorientation of the charges (X-Axis). As illustrated in FIG. 2A (0200)the variation of EHD is significant and ranges from 0.05 for a 300degree orientation charge to 0.32 for a 180 degree oriented charge. Thevariation of EHD makes a stage design unreliable and unpredictable forpressure and treatment of the stage. According to other studies thevariation of EHD is as much as +−50%. Therefore, there is a need for ashaped charge that can reliably and predictably create entrance holeswith a variation less than 7.5% irrespective of the severalaforementioned design and environmental factors.

FIG. 2B (0220) illustrates a chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versusorientation of the charges (X-Axis). Pressure drop through an entrancehole can vary as much as the variation in the EHD raised to the power offour. As illustrated in FIG. 2B (0220) the variation of pressure drop issignificant and can be as high as 500% for a 180 degree oriented charge.The variation of EHD creates a pressure that is more than designed fortreatment of the stage. In some cases the deviation of the pressure dropcan be as high as 500%. For example, if the designed pressure drop is1000 psi at a given pumping rate and if the perforated EHD is smallerthan targeted EHD due to the aforementioned factors then the actualpressure drop during treatment could be as high as 10000 psi. Therefore,there is a need for a shaped charge design that can reliably andpredictably create entrance holes with a predictable pressure drop at agiven rate. There is a need for designing a stage with a pressurevariation less than 500 psi between clusters irrespective of the severalaforementioned design and environmental factors.

FIG. 3 (0300) illustrates a chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versus water gapof the charges (X-Axis). As illustrated in FIG. 3 (0300) the variationof EHD is significant and ranges from 2% for a 0.2 inch water gap to 33%for a 1.2 inch water gap. The variation of EHD makes a stage designunreliable and unpredictable for pressure and treatment of the stage.According to other studies the variation of EHD is as much as +−50%.Therefore, there is a need for a shaped charge that can reliably andpredictably create entrance holes with a variation less than 7.5%irrespective of the water gap or clearance of the charges with respectto the casing.

Prior Art Stage Design and Perforation Method (0400)

As generally seen in the flow chart of FIG. 4 (0400), a prior art stagedesign and perforation method with conventional deep penetrating or bighole shaped charges may be generally described in terms of the followingsteps:

-   -   (1) Setting up a plug and isolating a stage in a well casing        (0401);    -   (2) Positioning a perforating gun system with shaped charges and        perforate (0402);    -   (3) Pumping fracture fluid in the stage and manually adjusting        pump rate based on the entrance hole diameters and perforation        tunnel width and length (0403); and        -   The perforation entrance holes created with conventional            charges are prone to unpredictable variation in diameter and            perforation tunnel length and diameter. The operator has to            increase pump rate in order to inject fluid through the            smaller entrance holes. Furthermore, a decentralized gun may            create a non-uniform hole size on the top and bottom of the            gun. In most cases, operators do not centralize the gun and            the pump rate is increased instead.    -   (4) Completing all stages.

Limited entry fracturing is based on the premise that every perforationwill be in communication with a hydraulic fracture and will becontributing fluid during the treatment at the pre-determined rate.Therefore, if any perforation does not participate, then the incrementalrate per perforation of every other perforation is increased, resultingin higher perforation friction. By design, each perforation in limitedentry is expected to be involved in the treatment. Currently, 2 to 4perforation holes per cluster, and 1 to 8 clusters per stage are shot sothat during fracturing treatment fluid is limited to the cluster at theheel end and the rest is diverted to the downstream (toe end) clusters.Some of the perforation tunnels with smaller EHD's than intended EHDcause energy and pressure loss during fracturing treatment which reducesthe intended pressure in the fracture tunnels. For example, if a 100 bpmfracture fluid is pumped into each stage at 10000 psi with an intentionto fracture each perforation tunnel at 2-3 bpm, most of the energy islost in ineffective fractures due to smaller EHD and higher tortuositythereby reducing the injection rate per fracture to substantially lessthan 2-3 bpm. The more energy put through each perforation tunnel, themore fluid travels through the fracture tunnel, the further the fractureextends. Most designs currently use unlimited stage entry to circumventthe issue of EHD variations in limited entry. However, unlimited entrydesigns are ineffective and mostly time expensive. In unlimited entrywhen one fracture takes up fracture fluid it will take up most of thefluid while the other tunnels are deprived of the fluid. Limited entrylimits the fluid entry into each cluster by limiting the number ofperforations per cluster, typically 2-3 per cluster. Therefore, there isa need for creating entrance holes with minimum variation of EHD (lessthan 7.5%) within a cluster and between clusters so that each of theclusters in the limited entry state contribute substantially equallyduring fracture treatment.

Some of the techniques currently used in the art for diverting fracturefluid include adding sealants such as ball sealers, solid sealers orchemical sealers that plug perforation tunnels so as to limit the flowrate through the heelward cluster and divert the fluid towards toewardclusters. However, if the EHD's and penetration depths of tunnels in theclusters have a wide variation, each of the clusters behave differentlyand the flow rate in each of the clusters is not controlled and notequal. Therefore, there is a need for more equal entry (EHD) design thatallows for a precise design for effective diversion. There is also aneed for a method that distributes fluid substantially equally amongvarious clusters in a limited entry stage.

Publications such as “Advancing Consistent Hole Charge Technology toImprove Well Productivity” (“IPS-10”) in INTERNATIONAL PERFORATINGSYMPOSIUM GALVESTON disclose shaped charges that create consistententrance holes. IPS-10 discloses a jet in slide 4 that illustrates acontrast of conventional shaped jet versus a jet created by consistenthole technology at a tail end of the jet. However, a constant jet at thetail end of a jet would not create constant diameter and widthperforation tunnel. Therefore, there is a need for a constant diameterjet (extended portion) between a tail end and a tip end of the jet sothat a constant diameter perforation tunnel is created along with aconstant diameter entrance hole. IPS-10 also discloses a table in slide16 illustrating a variation of entrance hole diameters for differentcompanies, gun diameters, casing diameters and charges. Company Acreates a hole size of 0.44 inches with a variation of 5.9% with a 3⅜inch gun size, 5½ inch casing; creates a hole size of 0.38 inches with avariation of 4.9% with a different charge. However, company A clearlydemonstrates a different hole size (0.44 inches vs. 0.38 inches) withidentical gun size and casing size. There is a need for creating anentrance hole with diameter that is unaffected by changes in the casingsize or the gun size.

Publications such as “Perforating Charges Engineered to OptimizeHydraulic Stimulation Outperform Industry Standard and Reactive LinerTechnology” (“IPS-11”) in INTERNATIONAL PERFORATING SYMPOSIUM GALVESTONteach low variability entrance holes (slide 5). However, the lowvariability is not associated with a wide subtended angle liner in acharge. IPS-11 does not teach a constant diameter and length penetratingjet along with a constant diameter entrance hole.

Hunting discloses (www.hunting-intl.com/titan) an EQUAfrac® ShapedCharge that reduces variation in entry holes diameters. According to thespecifications of the flyer, the variation of the charges for entrancehole diameters 0.40 inches and 0.38 inches are 2.5% and 4.9%. However,the penetration depth variation is quite large. Furthermore, EQUAfrac®Shaped Charge does not teach a subtended angle of liner greater than 90degrees. EQUAfrac® Shaped Charge does not teach a jet that can produce aconstant diameter jet that creates a perforation tunnel with a constantdiameter, length and width irrespective of design and environmentalfactors.

Typically deep penetrating charges are designed with a 40-60 degreeconical liner. Big hole charges typically comprise a liner with aparabolic or a hemispherical shape. The angle in the big hole rangesfrom 70-90 degrees. However, current art does not disclose charges thatcomprise liners with greater than 90 degree subtended angle. The jetformed by the deep penetrating and big hole charge is typically notconstant and a tip portion gets consumed in a water gap in the casingwhen a gun is decentralized. Operators in the field cannot centralize agun and therefore after perforation step, the diameter of the entrancehole at the bottom is much greater than the diameter of the hole in thetop. A portion of the tip of the jet is generally consumed in the watergap leaving a thin portion of the jet to create an entrance hole.Furthermore, the diameter and width of the jet may not be constant andtherefore a perforation tunnel is created with an unpredictablediameter, length and width. Therefore, there is a need for creatingequal diameter entrance holes in the top and bottom of a casingirrespective of the size of the water gap, the thickness of the casingand the composition of the casing. There is also a need for creating aconstant diameter jet that creates a perforation tunnel with a constantdiameter, width and length irrespective of the design and environmentalfactors such as casing diameter, gun diameter, a thickness of the wellcasing, composition of the well casing, position of the charge in theperforating gun, position of the perforating gun in the well casing, awater gap in the wellbore casing, or type of the hydrocarbon formation.

A step down rate test is typically used to pump fluid at various pumprates and record pressure at each of the rate. This type of analysis isperformed prior to a main frac job. It is used to quantify perforationand near-wellbore pressure losses (caused by tortuosity) of fracturedwells, and as a result, provides information pertinent to the design andexecution of the main frac treatments. Step-down tests can be performedduring the shut-down sequence of a fracture calibration test. To performthis test, a fluid of known properties (for example, water) is injectedinto the formation at a rate high enough to initiate a small frac. Theinjection rate is then reduced in a stair-step fashion, each ratelasting an equal time interval, before the well is finally shut-in. Theresulting pressure response caused by the rate changes is influenced byperforation and near-wellbore friction. Tortuosity and perforationfriction pressure losses vary differently with rate. By analyzing thepressure losses experienced at different rates, we can differentiatebetween pressure losses due to tortuosity and due to perforationfriction.

Pressure drops across perforations and due to tortuosity are givenmathematically by the following equations:

${\Delta\; p_{perf}} = {{k_{perf}q^{2}\mspace{14mu}{where}\mspace{14mu} k_{perf}} = \frac{1.975\gamma_{inj}}{C_{d}^{2}n_{perf}^{2}d_{perf}^{4}}}$Δ p_(tort) = k_(tort)q^(α)

-   -   Δp_(perf) Perforation pressure toss, psi    -   Δp_(tort) Tortuosity pressure loss, psi    -   q Flow rate, stb/d    -   k_(perf) Perforation pressure loss coefficient, psi/(stb/d)²    -   k_(tort) Tortuosity pressure miss coefficient, psi/stb/d)²    -   γ_(inj) Specific gray of injected fluid    -   C_(d) Discharge coefficient    -   n_(perf) Number of perforations    -   d_(perf) Diameter of perforation, in    -   α Tortuosity pressure loss exponent, usually 0.5

For step-down tests, it is essential to keep as many variablescontrolled as possible, so that the pressure response during the ratechanges is due largely to perforations and tortuosity, and not someother factors. When the injection rate is changed, the pressure does notchange in a stair-step fashion; it takes some time for pressure tostabilize after a change in rate. To make sure the effect of thispressure transition does not obscure the relationship between theinjection rate and pressure, injection periods of the same duration areused. From the equations aforementioned, one of key contributors to theperforation pressure loss is the diameter of the perforation hole. Alarge variation in the diameter of the perforation causes a largevariation in the perforation loss component. Therefore, there is a needto fix the perforation hole diameter within a variation of 7.5% inchessuch the overall pressure loss is attributable to the tortuosity andprovides a measure of the tortuosity near the wellbore.

Deficiencies in the Prior Art

The prior art as detailed above suffers from the following deficiencies:

-   -   Prior art systems do not provide for a shaped charge that can        reliably and predictably create entrance holes with a variation        less than 7.5% irrespective of the several aforementioned design        and environmental factors.    -   Prior art methods do not provide for designing a shaped charge        comprising a liner filled with an explosive such that the        resulting variation in the length and the width of perforation        tunnel is minimal.    -   Prior art methods do not provide for designing a stage with a        pressure variation less than 500 psi between clusters        irrespective of the several aforementioned design and        environmental factors.    -   Prior art methods do not provide for creating entrance holes        with minimum variation of EHD (less than 7.5%) within a cluster        and between clusters so that each of the clusters in the limited        entry state contribute substantially equally during fracture        treatment.    -   Prior art methods do not provide for more equal entry (EHD)        design that allows for a precise design for effective diversion.        There is also a need for a method that distributes fluid        substantially equally among various clusters in a limited entry        stage.    -   Prior art methods do not provide a shaped charge capable of        creating constant EHD's so that the tortuosity near a wellbore        can be determined or modelled.    -   Prior art methods do not provide a step down rate test with a        controlled and predictable pressure loss due to perforation        hole.    -   Prior art charges do not provide for a constant diameter jet        (extended portion) between a tail end and a tip end of the jet        so that a constant diameter, constant length perforation tunnel        is created along with a constant diameter entrance hole and        unaffected by design and environmental factors such as casing        diameter, gun diameter, a thickness of the well casing,        composition of the well casing, position of the charge in the        perforating gun, position of the perforating gun in the well        casing, a water gap in the wellbore casing, or type of the        hydrocarbon formation.

While some of the prior art may teach some solutions to several of theseproblems, the core issue of creating constant hole diameter entrancehole with a variation less than 7.5% has not been addressed by priorart.

BRIEF SUMMARY OF THE INVENTION System Overview

The present invention in various embodiments addresses one or more ofthe above objectives in the following manner. The present inventionprovides a shaped charge for use in a perforating gun is disclosed. Thecharge comprises a case, a liner positioned within the case, and anexplosive filled within the case. The liner is shaped with a subtendedangle about an apex, a radius, and an aspect ratio such that a jetformed with the explosive creates an entrance hole in a well casing. Thesubtended angle of the liner ranges from 100° to 120°. The jet creates aperforation tunnel in a hydrocarbon formation, wherein a diameter of thejet, a diameter of the entrance hole diameter, and a width and length ofthe perforation tunnel are substantially constant and unaffected withchanges in design and environmental factors such as a thickness andcomposition of the well casing, position of the charge in theperforating gun, position of the perforating gun in the well casing, awater gap in the wellbore casing, and type of the hydrocarbon formation.

Method Overview

The present invention system may be utilized in the context of anoverall perforating method with shaped charges in a perforating system,wherein the shaped charges as described previously is controlled by amethod having the following steps:

-   -   (1) setting up a plug and isolating a stage;    -   (2) targeting an entrance hole diameter of the entrance hole;    -   (3) selecting an explosive load, a subtended angle, a radius and        an aspect ratio for each of the plurality of charges;    -   (4) positioning the system along with the plurality of charges        in the well casing;    -   (5) perforating with the plurality of charges into a hydrocarbon        formation;    -   (6) creating the entrance hole with the entrance hole diameter        and completing the stage; and    -   (7) pumping fracture treatment in the stage at a designed rate        without substantially adjusting pumping rate.

Integration of this and other preferred exemplary embodiment methods inconjunction with a variety of preferred exemplary embodiment systemsdescribed herein in anticipation by the overall scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the advantages provided by the invention,reference should be made to the following detailed description togetherwith the accompanying drawings wherein:

FIG. 1 is a prior art perforating gun system in a well casing.

FIG. 2A is a prior art chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versusorientation of the charges (X-Axis).

FIG. 2B is a prior art chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versusorientation of the charges (X-Axis).

FIG. 3 is a prior art chart of entrance hole diameter variation (Y-Axis)for different entrance hole diameters (Y-Axis) versus water gap orclearance (X-Axis).

FIG. 4 is a prior art wellbore stage design method.

FIG. 5A is an exemplary side view of a shaped charge with a linersuitable for use in some preferred embodiments of the invention.

FIG. 5B is an exemplary side view of a big hole shaped charge with aliner suitable for use in some preferred embodiments of the invention.

FIG. 6 is an illustration of entrance holes with substantially equaldiameters and created by exemplary shaped charges according to apreferred embodiment of the present invention.

FIG. 7A is an exemplary chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versusorientation of the charges (X-Axis) as created by some exemplary chargesof the present invention.

FIG. 7B is an exemplary chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versusorientation of the charges (X-Axis) as created by some exemplary chargesof the present invention.

FIG. 8 is an exemplary chart of entrance hole diameter variation(Y-Axis) for different entrance hole diameters (Y-Axis) versus water gapof the charges (X-Axis) as created by some exemplary charges of thepresent invention.

FIG. 9 is an exemplary side view of a shaped charge with a liner in adecentralized perforating gun suitable for use in some preferredembodiments of the invention.

FIG. 10 is an illustration of a jet created by an exemplary shapedcharge according to a preferred embodiment of the present invention.

FIG. 11 is a detailed flowchart of a stage perforation method inconjunction with exemplary shaped charges according to some preferredembodiments.

FIG. 12 is a detailed flowchart of a limited entry method for treating astage in a well casing in conjunction with exemplary shaped chargesaccording to some preferred embodiments.

FIG. 13 is a detailed flowchart of a step down method for determiningtortuosity in a hydrocarbon formation in conjunction with exemplaryshaped charges according to some preferred embodiments.

DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetailed preferred embodiment of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit the broadaspect of the invention to the embodiment illustrated.

The numerous innovative teachings of the present application will bedescribed with particular reference to the presently preferredembodiment, wherein these innovative teachings are advantageouslyapplied to the particular problems of creating constant diameterentrance holes and constant diameter and length perforation tunnels.However, it should be understood that this embodiment is only oneexample of the many advantageous uses of the innovative teachingsherein. In general, statements made in the specification of the presentapplication do not necessarily limit any of the various claimedinventions. Moreover, some statements may apply to some inventivefeatures but not to others.

Objectives of the Invention

Accordingly, the objectives of the present invention are (among others)to circumvent the deficiencies in the prior art and affect the followingobjectives:

-   -   Provide for a shaped charge that can reliably and predictably        create entrance holes with a variation less than 7.5%        irrespective of the several aforementioned design and        environmental factors.    -   Provide for designing a shaped charge comprising a liner filled        with an explosive such that the resulting variation in the        length and the width of perforation tunnel is minimal.    -   Provide for designing a stage with a pressure variation less        than 500 psi between clusters irrespective of the several        aforementioned design and environmental factors.    -   Provide for creating entrance holes with minimum variation of        EHD (less than 0.05 inches) within a cluster and between        clusters so that each of the clusters in the limited entry state        contribute substantially equally during fracture treatment.    -   Provide for more equal entry (EHD) design that allows for a        precise design for effective diversion. There is also a need for        a method that distributes fluid substantially equally among        various clusters in a limited entry stage.    -   Provide a shaped charge capable of creating constant EHD's so        that the tortuosity near a wellbore can be determined or        modelled.    -   Provide a step down rate test with a controlled and predictable        pressure loss due to perforation hole.    -   Provide for a constant diameter jet (extended portion) between a        tail end and a tip end of the jet so that a constant diameter,        constant length perforation tunnel is created along with a        constant diameter entrance hole and unaffected by design and        environmental factors such as casing diameter, gun diameter, a        thickness of the well casing, composition of the well casing,        position of the charge in the perforating gun, position of the        perforating gun in the well casing, a water gap in the wellbore        casing, or type of the hydrocarbon formation.

While these objectives should not be understood to limit the teachingsof the present invention, in general these objectives are achieved inpart or in whole by the disclosed invention that is discussed in thefollowing sections. One skilled in the art will no doubt be able toselect aspects of the present invention as disclosed to affect anycombination of the objectives described above.

Preferred Exemplary System Shaped Charge and Perforating Jet

After a stage has been isolated for perforation, a perforating gunstring assembly (GSA) may be deployed and positioned in the isolatedstage. The GSA may include a string of perforating guns such as gunmechanically coupled to each other through tandems or subs or transfers.After a GSA is pumped into the wellbore casing, the GSA may bedecentralized on the bottom surface of the casing due to gravity. TheGSA may orient itself such that a plurality of charges inside a chargeholder tube (CHT) are angularly oriented or not. The plurality of shapedcharges in the gun together may herein be referred to as “cluster”. Thecharges may be oriented with a metal strip. The perforating guns may becentralized or decentralized in the casing. According to a preferredexemplary embodiment the thickness of the well casing ranges from 0.20to 0.75 inches. According to another preferred exemplary embodiment thediameter of the well casing ranges from 3 to 12 inches. According to amore preferred exemplary embodiment the diameter of the well casingranges from 4 to 6 inches.

FIG. 5A generally illustrates a cross section of an exemplary shapedcharge (0500) comprising a case (0501), a liner (0502) positioned withinthe case (0501), and an explosive (0503) filled between the liner (0502)and the case (0501). FIG. 5B generally illustrates a cross section of anexemplary big hole shaped charge (0540) comprising a case, a linerpositioned within the case, and an explosive filled between the linerand the case. According to a preferred exemplary embodiment, thethickness (0504) of the liner (0502) may be constant or variable. Thethickness of the liner may range from 0.01 inches to 0.2 inches. Theshaped charge may be positioned with a charge holder tube (not shown) ofa perforating gun (not shown). According to a preferred exemplaryembodiment the charge is a reactive or conventional charge. According toa preferred exemplary embodiment the diameter of the perforating gunranges from 1 to 7 inches. According to another preferred exemplaryembodiment the position of the charge in the perforating gun is orientedin an upward direction. According to yet another preferred exemplaryembodiment the position of the charge in the perforating gun is orientedin a downward direction. The liner may be shaped with a subtended angle(0513) about an apex (0510) of the liner (0502). The apex (0510) of theliner may be an intersecting point and the subtended angle (0513) may bean angle subtended about the apex (0510). The liner shape may have aradius (0512) and a height (0511). According to a preferred exemplaryembodiment the radius of the liner ranges from 0.01 to 0.5 inches. Anaspect ratio of the liner may be defined as a ratio of the radius (0512)to the height (0511) of the liner (0502). According to a preferredexemplary embodiment the aspect ratio of the liner ranges from 1 to 10.According to a more preferred exemplary embodiment the aspect ratio ofthe liner ranges from 2 to 5. According to a most preferred exemplaryembodiment the aspect ratio of the liner ranges from 3 to 4. The aspectratio, subtended angle (0513) and a load of explosive are selected suchthat a jet formed with the explosive creates an entrance hole in a wellcasing. The jet creates a perforation tunnel in a hydrocarbon formationafter penetrating through a casing. The casing may be cemented or not.The jet may also penetrate a water gap within the casing. The diameterof the jet, a diameter of the entrance hole, and a width and length ofthe perforation tunnel are substantially constant and unaffected withchanges in design and environmental factors. The design andenvironmental factors are selected from a group comprising of: a casingdiameter, a gun diameter, a thickness of the well casing, composition ofthe well casing, position of the charge in the perforating gun, positionof the perforating gun in the well casing, a water gap in the wellborecasing, type of said hydrocarbon formation, or a combination thereof. Ifa shaped charge is designed to create a 0.35 inch entrance hole diameter(0.35 EHD) or a 0.40 inch entrance hole diameter (0.40 EHD), the aspectratio, subtended angle, and/or an explosive load weight is selected foreach shaped charge depending on the entrance hole diameter. According toa preferred exemplary embodiment the diameter of the entrance hole inthe well casing ranges from 0.15 to 0.75 inches. The 0.35 EHD chargecreates an entrance hole in a casing with a substantially constant 0.35inch diameter and the 0.40 charge creates an entrance hole in a casingwith a substantially constant 0.40 inch diameter regardless of changesin the aforementioned design and environmental factors. It should benoted that the term “water gap” used herein is a difference of theoutside diameter of a perforating gun and the inside diameter of acasing. According to a preferred exemplary embodiment said thickness ofsaid water gap (diff ranges from 0.15 to 2.5 inches. For example, if theperforating gun with a 3 ½ inch outside diameter is decentralized andlays at the bottom of a casing with an inside diameter of 5½ inches, thewater gap is 2 inches. In some instances, if the water gap changes from1 inches to 4 inches or thickness of the casing changes from 0.6 inchesto 1 inch, the 0.35 EHD charge may create an entrance hole that has adiameter that ranges from 0.32375 to 0.37625 inches for both the watergaps or in other words the variation is less than 7.5%. Similarly, the0.40 EHD charge will create a 0.40 in diameter entrance hole for boththe water gaps and both the thicknesses of the casing with a variationless than 7.5%. The variation of the EHD 7.5% and the variation of theperforation length is less than 5% for perforating into any hydrocarbonformation. According to a preferred exemplary embodiment the type of thehydrocarbon formation is selected from a group comprising: shale,carbonate, sandstone or clay.

FIG. 6 (0600) generally illustrates entrance holes for 0.30 EHD charges(0601), 0.35 EHD charges (0602) and 0.40 EHD charges (0603). Theentrance holes of each of the charges are illustrated for phasing of 0°,60°, 120°, 180°, 240°, 300°, and 360°. The variation of 0.30 EHD charges(0601), 0.35 EHD charges (0602) and 0.40 EHD charges (0603) at thevarious phasing is less than 7.5% and in most cases less than 5%. FIG.7A (0700) generally illustrates an exemplary flow chart of a 0.40 EHDcharge in a 5½ inch casing. The chart shows the entrance hole diameters(0702) on the Y-Axis for different phasing on the X-Axis (0701).Additionally, a variation of the entrance hole diameters (0703) as apercentage is generally illustrated on the Y-Axis for different phasingon the X-Axis (0701). As illustrated the variation of EHD for the 0.40EHD charge is less than 5% for all the different phasing's. It should benoted the variation is unaffected by variation in water gaps in thecasing. Similar charts of 0.30 EHD charge (not shown), 0.35 EHD charge(not shown) and other EHD charges (not shown) illustrate a variation inEHD of less than 5%. The variation of EHD created by prior art chargesas illustrated in FIG. 2A (0200) is more than 30%.

FIG. 7B (0800) generally illustrates an exemplary flow chart of a 0.40EHD charge in a 5½ inch casing. The chart shows the entrance holediameters (0802) on the Y-Axis for different phasing (degree oforientation) on the X-Axis (0801). Additionally, a variation of thepressure (0803) as a percentage of designed pressure is generallyillustrated on the Y-Axis for different phasing on the X-Axis (0801). Asillustrated the variation of pressure drop for the 0.40 EHD charge isless than 100% for all the different phasing's. It should be noted thevariation of pressure is unaffected by variation in water gaps in thecasing. For example, the pressure drop may be less than 1000 psi for adesigned pressure of 500 psi. The amount of pressure required to injectfluid at a given rate varies as the fourth power of EHD of the holes andmay be directly proportional to the variation of the penetration lengthof the tunnel. According to an exemplary embodiment, an exemplary shapedcharge is configured with a subtended angle, explosive weight such thata jet created from the shaped charge creates a substantially constantdiameter entrance hole and a substantially constant penetration depthand diameter of the perforation tunnel in a hydrocarbon formation. Thevariation of pressure drop by prior art charges as illustrated in FIG.2B (0220) is more than 450%.

FIG. 8 (0820) generally illustrates an exemplary flow chart of a 0.40EHD charge in a 5½ inch casing. The chart shows the entrance holediameters (0812) on the Y-Axis for water gaps on the X-Axis (0811).Additionally, a variation of the entrance hole diameters (0813) as apercentage is generally illustrated on the Y-Axis for different watergap clearances on the X-Axis (0811). As illustrated the variation of EHDfor the 0.40 EHD charge is less than 5% for all the different watergaps. It should be noted the variation is unaffected by variation inphasing of the charges in the casing. Similar charts of 0.30 EHD charge(not shown), 0.35 EHD charge (not shown) and other EHD charges (notshown) illustrate a variation in EHD of less than 5%. The variation ofEHD created by prior art charges as illustrated in FIG. 3 (0300) is morethan 30%. For example, for a water gap of 1.2 inches, prior art chargesshow a variation of 33% versus 4.9% variation created by exemplarycharges illustrated in FIG. 5A (0500) and FIG. 5B (0540).

As shown below in Table 1.0, the 0.30 EHD charge, 0.35 EHD charge andthe 0.40 EHD charge create entrance holes corresponding to 0.30 in, 0.35in and 0.40 in with a variation of 3.8%, 3.0% and 3.8% respectively.According to a preferred exemplary embodiment, the variation ((maximumdiameter−minimum diameter/average diameter)*100) of the entrance holediameters is less than 7.5%. In other cases, the variation is less than0.02 inches of the target EHD. Additionally, each of the charges createa penetration length of 7 inches irrespective of the other factorsindicated such as gun outer diameter, shot density and phasing, entryhole diameter, and casing diameter. It should be noted that severalother factors such as aforementioned design and environmental factors donot impact the penetration length and diameter of the perforationtunnel. While prior art such as aforementioned IPS-10 and IPS-11illustrate low variability, the variability of penetration length of theperforation tunnel is not shown. Preferred embodiments as illustrated inTABLE 1.0 illustrate a variation of less than 5% for entrance holediameters and a substantially constant penetration length irrespectiveof other factors such as aforementioned design and environmentalfactors. According to a preferred exemplary embodiment the length ofsaid perforation tunnel in the hydrocarbon formation ranges from 1 to 20inches. According to another preferred exemplary embodiment a variationof the length of the perforation tunnel in the hydrocarbon formation isless than 20%. According to yet another preferred exemplary embodiment avariation of the width of the perforation tunnel in the hydrocarbonformation range is less than 5%. The variation of the width of thetunnel may range from 2% to 10%. For example, for a 6 inch length tunnelthe length of the tunnel may range from 4.8-7.2 inches or +−1.2.According to yet another a preferred exemplary embodiment the width ofsaid perforation tunnel in said hydrocarbon formation ranges from 0.15to 1 inches. The subtended angle of the liner may be selected to createa constant diameter jet which in turn creates a constant diameter,length and width of the perforation tunnel. A constant diameter jetenables a substantially constant diameter entrance hole on the top andbottom of the casing irrespective of the water gap.

FIG. 9 (0900) generally illustrates a cross section of a perforating gun(0902) having a shaped charge (0903) with a liner (0904) and deployed ina well casing (0901). The liner may be designed with a subtended angle(0905). FIG. 9 (0900) also illustrates a water gap (0906) which isdefined as the difference in the inside diameter of the casing (0901)and the outside diameter of the perforating gun (0902). A ratio (EHDratio) of the diameter of the entrance hole of the top (0910) to theentrance hole of the bottom (0920) can be controlled by varying thesubtended angle and aspect ratio of the liner (0904). According to apreferred exemplary embodiment, the EHD ratio is less than 1 for asubtended angle of the liner between 90° and 100°. According to anotherpreferred exemplary embodiment, the EHD ratio is almost equal to 1 for asubtended angle of the liner between 100° and 110°. According to yetanother preferred exemplary embodiment, the EHD ratio is greater than 1for a subtended angle of the liner greater than 110°. According to apreferred exemplary embodiment, the subtended angle of the liner isbetween 90° and 120°. According to a more preferred exemplaryembodiment, the subtended angle of the liner is between 100° and 120°.According to a most preferred exemplary embodiment, the subtended angleof the liner is between 108° and 112°. A subtended angle of 110° mayresult in an EHD ratio of 1.

TABLE 1.0 Shot Gun Explosive Density Entry Rock API 19B EHD O.D. Weight(spf) Hole Penetration Targeted Variation Charge (in.) (g) Phasing (in.)(in.) Pipe Decentralized 0.30 3 16 6 spf 60 0.30 7 5½ in. 3.8% EHD ⅛ OD,23# P-110 0.35 3 20 6 spf 60 0.35 7 5½ in. 3.0% EHD ⅛ OD, 23# P-110 0.403 23 6 spf 60 0.40 7 5½ in. 3.8% EHD ⅛ OD, 23# P-110

FIG. 10 (1000) generally illustrates a shape of an exemplary jet createdby an exemplary shaped charge for use in a perforating gun, the chargecomprising a case, a liner positioned within the case, and an explosivefilled between the case and the liner. The liner may be shaped with asubtended angle about an apex of the liner, a radius, and an aspectratio such that the explosive forms a constant jet when exploded. Thejet (1000) further comprising a tip end (1001), a tail end (1003), andan extended portion (1002) positioned between the tail end and the tipend. A diameter (1004) of the extended portion is substantially constantfrom about the tip end to about the tail end. The diameter of anentrance hole diameter created by the jet (1000) is substantiallyconstant and unaffected with changes in design and environmentalfactors. The extended portion (1002) in the jet (1000) is unannihilatedin a water gap when the jet travels through a water gap in a casing. Thewater gap may be similar to the water gap (0906) illustrated in FIG. 9.The perforating gun may centralized in the casing. The perforating gunmay be decentralized in the casing as shown in FIG. 9. The velocity ofthe tip end may be slightly greater than a velocity of the tail end sothat the extended portion is substantially not stretched and thereforemaintaining a constant diameter after entry into a hydrocarbon formationuntil the tip end enters the formation. Additionally, the extendedportion is substantially not stretched and maintain a constant diameterbefore entry into a hydrocarbon formation until the tip end enters theformation. According to a preferred exemplary embodiment the diameter ofthe jet ranges from 0.15 to 0.75 inches. According to another preferredexemplary embodiment a variation of the diameter of the jet is less than5%. Constant EHD charges are uniquely designed and engineered to form aconstant diameter (1004) fully developed jet. The formation of the jetoccurs in the charge case and near the inside wall of the gun carrierbehind the scallop/spotface. The diameter of the jet in the initial (jetformation) region or tip end (1001) may be larger than the diameterafter it has been fully developed. The holes in the carrier and thecasing are formed by different parts of the perforating jet. Differentparts of the jets have different diameters. The hole in the gun carriermay be formed during the jet formation process and is comparativelylarger than the hole formed in the casing by the fully developed jet.The hole size in the carrier may be 65% larger than the hole size in thecasing. The hole size in the gun typically has no relation to the holesize in the casing. This phenomenon is expected and is indicative ofproper function.

Preferred Exemplary Flowchart Embodiment of a Stage Perforation Method(1100)

As generally seen in the flow chart of FIG. 11 (1100), a preferredexemplary wellbore perforation method with a plurality of exemplaryshaped charges; each of the plurality of charges configured to create anentrance hole in the casing; each of the plurality of charges areconfigured with liner having a subtended angle about an apex of theliner; the subtended angle of the liner ranges from 100° to 120°; avariation of diameters of entrance holes created with the plurality ofcharges is configured to be less than 7.5% and the variation unaffectedby design and environmental variables. The method may be generallydescribed in terms of the following steps:

-   -   (1) Setting up a plug and isolating a stage (1101);    -   (2) Targeting an entrance hole diameter of the entrance hole        (1102); Entrance hole diameters in the range of 0.15 to 0.75        inches may be targeted.    -   (3) Selecting an explosive load, a subtended angle, a radius and        an aspect ratio for each of the plurality of charges (1103);        -   The explosive load may be selected to create the targeted            hole size. For example as illustrated in Table 1.0,            explosive weights of 16 g, 20 g and 23 g create entrance            holes with diameters of 0.30 inches, 0.35 inches and 0.40            inches respectively. Other explosive weights may be chosen            to create EHD's from 0.15 to 0.75 inches. The subtended            angle of the liner may be selected to create a constant            diameter jet which in turn creates a constant diameter,            length and width of the perforation tunnel. A constant            diameter jet such as FIG. 10 (1000) enables a substantially            constant diameter entrance hole on the top and bottom of the            casing irrespective of the water gap such as FIG. 9 (0906).    -   (4) Positioning the system along with the plurality of charges        in the well casing (1104);    -   (5) Perforating with the plurality of charges into a hydrocarbon        formation (1105);    -   (6) Creating the entrance hole with the entrance hole diameter        and completing the stage (1106); and        -   The variation may be defined as ((Max. Diameter−Min.            Diameter/Avg. Diameter)*100). According to a preferred            exemplary embodiment, the variation of the entrance hole            diameters is less than 7.5% irrespective of the design and            environmental factors. According to a more preferred            exemplary embodiment, the variation of the entrance hole            diameters is less than 5%. In addition, the variation of the            length of the perforation tunnel may be less than 20%.    -   (7) Pumping fracture treatment in said stage at a designed rate        without substantially adjusting pumping rate (1107).        -   A substantially constant (variation less than 7.5%) entrance            hole diameter with a substantially constant penetration            length of the perforation tunnel enables a fracture            treatment at a designed injection rate without an operator            adjusting the pumping rate. The lower variation keeps the            pressure within 100% of the designed pressure as opposed to            500% for perforations created with conventional deep            penetration charges.

Preferred Exemplary Flowchart Embodiment of Limited Entry Perforation(1200)

Limited entry perforation provides an excellent means of divertingfracturing treatments over several zones of interest at a giveninjection rate. In a given hydrocarbon formation multiple fractures arenot efficient as they create tortuous paths for the fracturing fluid andtherefore result in a loss of pressure and energy. In a given wellbore,it is more efficient to isolate more zones with clusters comprising lessshaped charges as compared to less zones with clusters comprising moreshaped charges. For example, at a pressure of 10000 psi, to achieve 2barrels per minute flow rate per perforation tunnel, 12 to 20 zones and12-15 clusters each with 15-20 shaped charges are used currently.Instead, to achieve the same flow rate, a more efficient method andsystem is isolating 80 zones with more clusters and using 2 or 4 shapedcharges per cluster while perforating. Conventional perforating systemsuse 12-15 shaped charges per cluster while perforating in a 60/90/120degrees or a 0/180 degrees phasing. This creates multiple fractureplanes that are not efficient for fracturing treatment as the fracturingfluid follows a tortuous path while leaking energy/pressure intended foreach fracture. Creating minimum number of multiple fractures near thewellbore is desired so that energy is primarily focused on the preferredfracturing plane than leaking off or losing energy to undesiredfractures. 60 to 80 clusters with 2 or 4 charges per cluster may be usedin a wellbore completion to achieve maximum efficiency during oil andgas production.

As generally seen in the flow chart of FIG. 12 (1200), a preferredexemplary wellbore perforation method with an exemplary system; thesystem comprising a plurality of shaped charges configured to bearranged in a plurality of clusters, each of the plurality of charges isconfigured to create an entrance hole in the casing; each of theplurality of charges are configured with liner having a subtended angleabout an apex of the liner; the subtended angle of the liner ranges from100° to 120°; a variation of diameters of entrance holes created withthe plurality of charges within each of the plurality of clusters isconfigured to be less than 7.5% and the variation unaffected by designand environmental variables. According to a preferred exemplaryembodiment a number of clusters in each stage ranges from 2 to 10. Themethod may be generally described in terms of the following steps:

-   -   (1) Setting up a plug and isolating a stage (1201);        -   When a long lateral casing is installed, friction losses            within the pipe requires a larger entrance hole at the toe            end of the stage. Current stages are designed for more than            the required entrance hole. For example, a 0.45 EHD hole may            be designed when a 0.35 EHD is required due to            unpredictability of the EHD. An exemplary embodiment with a            low variability charges does not require over design of the            charges for EHD to overcome friction losses in a casing.    -   (2) Determining a target diameter for the entrance hole (1202);        -   Entrance hole diameters in the range of 0.15 to 0.75 inches            may be targeted. According to a preferred exemplary            embodiment the diameters of the entrance holes in all of the            clusters is substantially equal. According to another            preferred exemplary embodiment the target entrance hole            diameter in one of the plurality of clusters and another            said plurality of clusters is unequal. For example, if there            are 3 clusters in a stage, the target diameters of the            entrance holes created by all the charges in each cluster            may be 0.30 inches, 0.35 inches and 0.45 inches starting            from uphole to downhole. This step up diameter arrangement            of different EHD charges from uphole to downhole enables            fluid to be limited in the smallest hole and diverted to the            next biggest hole and further diverted to the largest hole.            In the above example, fluid is limited in the cluster with            the 0.30 inch hole and then diverted to 0.35 inch hole and            further diverted to 0.40 inch hole. The predictability and            low variability of the entrance holes enable the pumping            rate to be substantially (something missing) at the designed            pump rate. According to a preferred exemplary embodiment            each of the clusters is fractured at a fracture pressure; a            variation of the fracture pressure for all of the clusters            is configured to be less than 500 psi. For example, if the            designed pressure for a given injection rate is 5000 psi,            the variation of pressure is less than 500 psi or a range of            4500 to 5500 psi.    -   (3) Selecting an explosive load, a subtended angle, a radius and        an aspect ratio for each of the plurality of charges (1203);        -   The explosive load may be selected to create the targeted            hole size. For example as illustrated in Table 1.0,            explosive weights of 16 g, 20 g and 23 g create entrance            holes with diameters of 0.30 inches, 0.35 inches and 0.40            inches respectively. Other explosive weights may be chosen            to create EHD's from 0.15 to 0.75 inches. The subtended            angle of the liner may be selected to create a constant            diameter jet which in turn creates a constant diameter,            length and width of the perforation tunnel. A constant            diameter jet such as FIG. 10 (1000) enables a substantially            constant diameter entrance hole on the top and bottom of the            casing irrespective of the water gap such as FIG. 9 (0906).    -   (4) Positioning the system along with the plurality of charges        in the well casing (1204);        -   According to a preferred exemplary embodiment a target            entrance hole diameter of an entrance hole created in a toe            end cluster and a target entrance hole diameter of an            entrance hole created in a another cluster positioned            upstream of the toe end cluster are selected such that a            friction loss of the casing during the pumping step (8) is            offset. For example in aforementioned step (2), the toe end            cluster may have an EHD of 0.45 inches and the heel end            cluster may have an EHD of 0.35 inches and the friction loss            of the casing may be offset by the difference of the            predictable EHD of the toe end and heel end clusters. The            pressure drop and pumping rate of the fluid may be kept with            a 1000 psi range while also accounting for the friction            loss.    -   (5) Perforating with the plurality of charges into a hydrocarbon        formation and creating a jet with each of the plurality of        charges (1205);    -   (6) Creating the entrance hole with the target entrance hole        diameter with the jet (1206);    -   (7) Creating a perforation tunnel with the jet; each of the        perforation tunnels configured with substantially equal width        and length (1207);        -   According to a preferred exemplary embodiment a variation of            perforation length with the plurality of charges within each            of the plurality of clusters is configured to be less than            20%. Similarly, a variation of perforation width with the            plurality of charges within each of the plurality of            clusters is configured to be less than 20%.    -   (8) Pumping fracture treatment in the stage at a designed rate        without substantially adjusting pumping rate (1208); and    -   (9) Diverting fluid substantially equally among the plurality of        clusters (1209).        -   According to a preferred exemplary embodiment diverters are            pumped along with the pumping fluid in the pumping step (8).            The diverters may be selected from a group comprising: solid            diverters, chemical diverters, or ball sealers. For a            limited entry treatment, it is important that each of the            clusters participate equally in the fracture treatment.            Fluid is pumped at a high rate and the number of cluster are            limited so that the amount of fluid in each of the clusters            is limited. According to a preferred exemplary embodiment, a            substantially constant entrance hole along with diverters            enables fluid to be limited and equally diverted among the            clusters. According to another preferred exemplary            embodiment a number of the plurality of charges in each of            the clusters is further based on the target entrance hole            diameter. For example, if the number of clusters is 10 the            target diameter may be 0.30 inches to achieve maximum            fracture efficiency. Alternatively, the number of clusters            may be 5 the target diameter may be 0.45 inches to achieve a            similar maximum fracture efficiency. The design of the EHD,            the number of charges per cluster, the number of clusters            per stage and the number of stages per zone can be factored            in with the predictable variation of entrance hole diameters            to achieve maximum perforation and fracture efficiency.

Preferred Exemplary Flowchart Embodiment of a Step Down Method (1300)

Step-down test analysis is done by plotting the pressure/rate datapoints with the same time since the last rate change on a pressure-rateplot, and matching the pressure loss model to these points. On the basisof the model, the perforation and tortuosity components of the pressureloss are calculated, and the defining parameters are also estimated.From the equations aforementioned, one of key contributors to theperforation pressure loss is the diameter of the perforation hole. Alarge variation in the diameter of the perforation causes a largevariation in the perforation loss component. The exemplary chargesillustrated in FIG. 5A (0500) or FIG. 5B (0540) create EHD's within avariation of 7.5% such that overall pressure loss is attributable to thetortuosity and provides a measure of the tortuosity near the wellbore.When a tortuosity of the near wellbore is modelled, a stage may bedesigned with more accuracy and predictability. For step-down tests, itis essential to keep as many variables controlled as possible, so thatthe pressure response during the rate changes is due largely toperforations and tortuosity, and not some other factors. However, if thepressure variation due to perforations is controlled with exemplarycharges illustrated in FIG. 5A (0500) or FIG. 5B (0540), the pressureresponse during the rate changes is mainly due to tortuosity.

As generally seen in the flow chart of FIG. 13 (1300), a step downmethod for determining tortuosity in a hydrocarbon formation, inconjunction with a perforating gun system deployed in a well casing; thesystem comprising a plurality of shaped charges wherein, each of theplurality of charges are configured to create an entrance hole in acasing with a desired entrance hole diameter; each of the plurality ofcharges are configured with liner having a subtended angle about an apexof the liner; the subtended angle of the liner ranges from 100° to 120°;and a variation of diameters between each of the entrance hole is lessthan 7.5% and the variation unaffected by design and environmentalvariables. The method may be generally described in terms of thefollowing steps:

-   -   (1) Setting up a plug and isolating a stage (1301);    -   (2) Targeting an entrance hole diameter of the entrance hole        (1302); Entrance hole diameters in the range of 0.15 to 0.75        inches may be targeted.    -   (3) Selecting an explosive load, a subtended angle, a radius and        an aspect ratio for each of the plurality of charges (1303);    -   (4) Positioning the system along with the plurality of charges        in the well casing (1304);    -   (5) Perforating with the plurality of charges into a hydrocarbon        formation (1305);    -   (6) Creating the entrance hole with the entrance hole diameter        and completing the stage (1306);    -   (7) Pumping treatment fluid at different fluid rates into the        perforation tunnel in the stage (1307);    -   (8) Recording pressure at each of the fluid rates (1308); and    -   (9) Calculating tortuosity of the formation based on a pressure        loss due to well friction (1309).

System Summary

The present invention system anticipates a wide variety of variations inthe basic theme of a shaped charge for use in a perforating gun, thecharge comprising a case, a liner positioned within the case, and anexplosive filled within the liner; the liner shape configured with asubtended angle about an apex of the liner, a radius, and an aspectratio such that a jet formed with the explosive creates an entrance holein a well casing; the subtended angle of the liner ranges from 100° to120°; the jet creates a perforation tunnel in a hydrocarbon formation;wherein a diameter of the jet, a diameter of the entrance hole, and awidth and length of the perforation tunnel are substantially constantand unaffected with changes in design and environmental factors.

An alternate invention system anticipates a wide variety of variationsin the basic theme of a shaped charge for use in a perforating gun, thecharge comprising a case, a liner positioned within the case, and anexplosive filled within the liner; the liner shape configured with asubtended angle about an apex of the liner, a radius, and an aspectratio such that a jet formed with the explosive creates an entrance holein a well casing; the jet creates a perforation tunnel in a hydrocarbonformation; wherein a diameter of the jet, a diameter of the entrancehole, and a width and length of the perforation tunnel are substantiallyconstant and unaffected with changes in design and environmentalfactors.

This general system summary may be augmented by the various elementsdescribed herein to produce a wide variety of invention embodimentsconsistent with this overall design description.

Method Summary

The present invention method anticipates a wide variety of variations inthe basic theme of implementation, but can be generalized as stageperforation method using a perforating gun system in a wellbore casingwherein the system comprises a plurality of shaped charges; each of theplurality of charges are configured to create an entrance hole in thecasing; a range of diameters of entrance holes created with theplurality of charges is configured to be less than 7.5% and thevariation unaffected by design and environmental variables;

wherein the method comprises the steps of:

-   -   (1) setting up a plug and isolating a stage;    -   (2) targeting an entrance hole diameter of the entrance hole;    -   (3) selecting an explosive load, a subtended angle, a radius and        an aspect ratio for each of the plurality of charges;    -   (4) positioning the system along with the plurality of charges        in the well casing;    -   (5) perforating with the plurality of charges into a hydrocarbon        formation;    -   (6) creating the entrance hole with the entrance hole diameter        and completing the stage; and    -   (7) pumping fracture treatment in the stage at a designed rate        without substantially adjusting pumping rate.

This general method summary may be augmented by the various elementsdescribed herein to produce a wide variety of invention embodimentsconsistent with this overall design description.

System/Method Variations

The present invention anticipates a wide variety of variations in thebasic theme of oil and gas extraction. The examples presented previouslydo not represent the entire scope of possible usages. They are meant tocite a few of the almost limitless possibilities.

This basic system and method may be augmented with a variety ofancillary embodiments, including but not limited to:

-   -   An embodiment wherein diameter of the jet, a diameter of the        entrance hole, and a width and length of the perforation tunnel        are substantially constant and unaffected by design and        environmental factors; the design and environmental factors        selected from a group comprising: casing diameter, gun diameter,        a thickness of the well casing, composition of the well casing,        position of the charge in the perforating gun, position of the        perforating gun in the well casing, a water gap in the well        casing, or type of the hydrocarbon formation.    -   An embodiment wherein a thickness of the liner is substantially        constant.    -   An embodiment wherein the thickness of the liner ranges from        0.01 to 0.2 inches.    -   An embodiment wherein the aspect ratio of the liner ranges from        2 to 5 inches.    -   An embodiment wherein the radius of the liner ranges from 0.01        to 0.5 inches.    -   An embodiment wherein the diameter of the entrance hole in the        well casing ranges from 0.15 to 0.75 inches.    -   An embodiment wherein a variation of the diameter of the        entrance hole in the well casing is less than 7.5% inches.    -   An embodiment wherein the width of the perforation tunnel in the        hydrocarbon formation ranges from 0.15 to 1 inches.    -   An embodiment wherein a variation of the width of the        perforation tunnel in the hydrocarbon formation ranges is less        than 5%.    -   An embodiment wherein the length of the perforation tunnel in        the hydrocarbon formation ranges from 1 to 20 inches.    -   An embodiment wherein a variation of the length of the        perforation tunnel in the hydrocarbon formation is less than        20%.    -   An embodiment wherein the diameter of the jet ranges from 0.15        to 0.75 inches.    -   An embodiment wherein a variation of the diameter of the jet is        less than 5%.    -   An embodiment wherein the thickness of the well casing ranges        from 0.20 to 0.75 inches.    -   An embodiment wherein the diameter of the well casing ranges        from 4 to 6 inches.    -   An embodiment wherein the diameter of the gun ranges from 1 to 7        inches.    -   An embodiment wherein the position of the charge in the        perforating gun is oriented in an upward direction.    -   An embodiment wherein the position of the charge in the        perforating gun is oriented in a downward direction.    -   An embodiment wherein the position of the perforating gun in the        well casing is centralized.    -   An embodiment wherein the position of the perforating gun in the        well casing is decentralized.    -   An embodiment wherein the thickness of the water gap ranges from        0.15 to 2.5 inches.    -   An embodiment wherein the type of the hydrocarbon formation is        selected from a group comprising: shale, carbonate, sandstone or        clay.    -   An embodiment wherein the charge is selected from a group        comprising: reactive, or conventional charges.

One skilled in the art will recognize that other embodiments arepossible based on combinations of elements taught within the aboveinvention description.

CONCLUSION

A shaped charge for use in a perforating gun has been disclosed. Thecharge comprises a case, a liner positioned within the case, and anexplosive filled within the case. The liner is shaped with a subtendedangle about an apex, a radius, and an aspect ratio such that a jetformed with the explosive creates an entrance hole in a well casing. Thejet creates a perforation tunnel in a hydrocarbon formation, wherein adiameter of the jet, a diameter of the entrance hole diameter, and awidth and length of the perforation tunnel are substantially constantand unaffected with changes in design and environmental factors such asa thickness and composition of the well casing, position of the chargein the perforating gun, position of the perforating gun in the wellcasing, a water gap in the wellbore casing, and type of the hydrocarbonformation.

What is claimed is:
 1. A shaped charge for use in a perforating gun, said charge comprising: a case, a liner positioned within said case, and an explosive filled within said liner; said liner shape configured with a subtended angle about an apex of said liner such that a jet formed with said explosive creates an entrance hole in a well casing; said subtended angle of said liner is larger than 90° and smaller than 120°; said liner having an exterior surface, said exterior surface substantially straight and conically tapered to form said apex; said jet creates a perforation tunnel in a hydrocarbon formation; wherein a diameter of said jet is substantially equal to a diameter of a second jet created by a second shaped charge, a diameter of said entrance hole is substantially equal to a diameter of a second entrance hole created by said second shaped charge, and a width and length of said perforation tunnel are substantially equal to a width and length of a second perforation tunnel created by said second shaped charge.
 2. The shaped charge of claim 1 wherein a thickness of said liner is substantially constant.
 3. The shaped charge of claim 1 wherein said diameter of said entrance hole in said well casing ranges from 0.15 to 0.75 inches.
 4. The shaped charge of claim 1 wherein a variation of said diameter of said entrance hole in said well casing is less than 7.5%.
 5. The shaped charge of claim 1 wherein said width of said perforation tunnel in said hydrocarbon formation ranges from 0.15 to 1 inches.
 6. The shaped charge of claim 1 wherein a variation of said width of said perforation tunnel in said hydrocarbon formation ranges is less than 5%.
 7. The shaped charge of claim 1 wherein said length of said perforation tunnel in said hydrocarbon formation ranges from 1 to 20 inches.
 8. The shaped charge of claim 1 wherein a variation of said length of said perforation tunnel in said hydrocarbon formation is less than 20%.
 9. The shaped charge of claim 1 wherein said diameter of said jet ranges from 0.15 to 0.75 inches.
 10. The shaped charge of claim 1 wherein a variation of said diameter of said jet is less than 5%.
 11. The shaped charge of claim 1 wherein a thickness of said well casing ranges from 0.20 to 0.75 inches.
 12. The shaped charge of claim 1 wherein a diameter of said well casing ranges from 4 to 6 inches.
 13. The shaped charge of claim 1 wherein a diameter of said gun ranges from 3 to 12 inches.
 14. The shaped charge of claim 1 wherein a position of said charge in said perforating gun is oriented in an upward direction.
 15. The shaped charge of claim 1 wherein a position of said charge in said perforating gun is oriented in a downward direction.
 16. The shaped charge of claim 1 wherein a position of said perforating gun in said well casing is centralized.
 17. The shaped charge of claim 1 wherein a position of said perforating gun in said well casing is decentralized.
 18. The shaped charge of claim 1 wherein a thickness of a water gap ranges from 0.15 to 2.5 inches.
 19. The shaped charge of claim 1 wherein a type of said hydrocarbon formation is selected from a group comprising: shale, carbonate, sandstone or clay.
 20. The shaped charge of claim 1 wherein said charge is selected from a group comprising: reactive, or conventional charges.
 21. A shaped charge for use in a perforating gun, said charge comprising: a case, a liner positioned within said case, and an explosive filled between said case and said liner; said liner shape configured with a subtended angle about an apex of said liner such that said explosive forms a constant jet when exploded; said liner having an exterior surface, said exterior surface substantially straight and conically tapered to form said apex; said subtended angle of said liner is larger than 90° and smaller than 120°; said jet further comprising a tip end, a tail end, and an extended portion positioned between said tail end and said tip end; a diameter of said extended portion is substantially constant from about said tip end to about said tail end; and wherein a diameter of an entrance hole created by said jet is substantially equal to a diameter of a second entrance hole created by a second shaped charge.
 22. The shaped charge of claim 21 wherein said extended portion in said jet is unannihilated in a water gap when said jet travels through said water gap in said well casing.
 23. The shaped charge of claim 21 wherein a velocity of said tip end is slightly greater than a velocity of said tail end.
 24. The shaped charge of claim 21 wherein said extended portion is substantially not stretched; said extended portion maintaining said diameter after entry into a hydrocarbon formation until said tip end enters said formation.
 25. The shaped charge of claim 21 wherein said extended portion is substantially not stretched; said extended portion maintaining said diameter before entry into a hydrocarbon formation until said tip end enters said formation.
 26. A stage perforation method using a perforating gun system in a wellbore casing; said system comprising a plurality of shaped charges; each of said plurality of charges are configured to create an entrance hole in said casing; each of said plurality of charges are configured with a liner having a subtended angle about an apex of said liner; said liner having an exterior surface, said exterior surface substantially straight and conically tapered to form said apex; said subtended angle of said liner is larger than 90° and smaller than 120°; a variation of diameters of entrance holes created with said plurality of charges is configured to be less than 7.5%; wherein said method comprises the steps of: (1) setting up a plug and isolating a stage; (2) targeting an entrance hole diameter of said entrance hole; (3) selecting an explosive load, a subtended angle, a radius and an aspect ratio for each of said plurality of charges; (4) positioning said system along with said plurality of charges in said well casing; (5) perforating with said plurality of charges into a hydrocarbon formation; (6) creating said entrance hole with said entrance hole diameter and completing said stage; and (7) pumping fracture treatment in said stage at a designed rate without substantially adjusting pumping rate.
 27. A shaped charge for use in a perforating gun, said charge comprising: a case, a liner positioned within said case, and an explosive filled within said liner; said liner shape configured with a subtended angle about an apex of said liner such that a jet formed with said explosive creates an entrance hole in a well casing; said subtended angle of said liner is larger than 90° and smaller than 120°; said liner not substantially shaped elliptically, oval, or semi-oval; said jet creates a perforation tunnel in a hydrocarbon formation; wherein a diameter of said jet is substantially equal to a diameter of a second jet created by a second shaped charge in a second perforating gun, a diameter of said entrance hole is substantially equal to a diameter of a second entrance created by said second shaped charge in said second perforating gun, and a width and length of said perforation tunnel are substantially constant equal to a width and length of a second perforation tunnel created by said second shaped charge in said second perforating gun.
 28. The shaped charge of claim 27 wherein said second shaped charge is positioned in a second perforating gun. 